Numerical Simulation Of Gas-liquid Mixing In A Circulating Bioreactor

The synthesis of biodegradable material poly-?-hydroxybutyrate(PHB)from methane is of great significance for mitigating global warming and white pollution caused by greenhouse gases(methane).PHB(poly-?-hydroxybutyrate)is a new biodegradable polymer material developed rapidly.PHB accumulates in cells through high-density culture of methane-oxidizing bacteria.At present,the main bottleneck hindering the industrialized production of PHB from methane synthesis is the low solubility of methane in water and the low cell growth density.In this paper,FLUENT mumerical simulation method is used to observe and study the flow and mixing mechanism of methane and water in horizontal tubular loop bioreactor to optimum the structure size of each stage of the bioreactor.Finally it came true that high density culture of methane-oxidizing bacteria to the maximum,which can provide theoretical foundation for the realization of industrialized production.Considering the environment of cells life and the vulnerability of cells,both a hybrid structure of Venturi mixer and static mixer are adopted.A Venturi mixer for mixing methane and water was designed in this paper.The effects of methane velocity,water velocity,import angle,diameter of tubule and exit angle on mixing efficiency were investigated by FLUENT numerical simulation.Firstly,the influence of single factor on the mixing effect of Venturi mixer was investigated,and the influence rule of single factor on mixing was summarized.In order to obtain the best mixer structure,orthogonal test was used to find that the order of influence degree of each factor,that was:water velocity>exit angle>diameter of tubule>methane velocity>import angle.The response surface method and genetic algorithm were used to further consider the optimal structure parameters and process parameters.FLUENT simulation was used to compare the internal fluid flow state of SK and SX static mixers,and to determine the type and structure parameters of static mixers.Reference is given to the volume fraction of methane at the outlet and the turbulence performance in the mixer.The design of horizontal and vertical sections directly affects the production of methane-oxidizing bacteria in high-density culture in bioreactor.Because the length of horizontal section and the height of vertical section directly determine the volume of bioreactor.The influence of length and height of tube segment on volumetric mass transfer coefficient and turbulence performance needs to be considered.So the length-diameter ratio and height-diameter ratio were used as parameters to simulate the flow in horizontal and vertical sections in the horizontal tubular loop bioreactor and determine the length and height of the pipeline.Pipeline shape at elbow was selected between right-angle elbow and U-shaped pipe,comparing of flow conditions in two kinds of pipelines when they were placed horizontally and vertically.Taking gas holdup and turbulence performance as reference,the appropriate pipe shape was selected.Finally it provide theoretical basis for optimization of the bioreactor.